Subject: Weird bug in oblong casing??
Location: Southern California
October 13, 2012 1:24 am
I found this in my bathroom the other day. I looks to me like a larvae in some kind of sack/cocoon/casing thing. The casing is an oblong shape with two entry/exit holes on opposite sides. The bug inside comes halfway out occasionally, but never completely out. It moves very slowly and pulls the casing along with it, like a hermit crab. The bug itself looks like a tiny caterpillar, like it has many small legs. It appears to be wither white or a very pale yellow with black stripes. The casing is no more than half an inch long.
Thank you so much for your help!
This is a Case Bearing Moth Larva, Phereoeca uterella. According to BugGuide: “larvae feed on old spider webs; may also eat woolen goods of all kinds if the opportunity arises.” BugGuide also notes: “The larval case is silk-lined inside and open at both ends. The case is constructed by the earliest larval stage (1st instar) before it hatches, and is enlarged by each successive instar. In constructing the case, the larva secretes silk to build an arch attached at both ends to the substrate. Very small particles of sand, soil, iron rust, insect droppings, arthropod remains, hairs and other fibers are added on the outside. The inside of the arch is lined exclusively by silk, and is gradually extended to form a tunnel, while the larva stays inside. The tunnel is closed beneath by the larva to form a tube free from the substrate, and open at both ends. After the first case is completed, the larva starts moving around, pulling its case behind. With each molt, the larva enlarges its case. Later cases are flattened and widest in the middle, allowing the larva to turn around inside.” We suppose they can be considered Household Pests, especially based on this amazing photo from our archive.